Acidic compositions non-corrosive to metal surfaces



United States Patent 3,240,714 Patented Mar. 15, 1966 "ice wherein R, R and n are as previously defined.

When X is sulfur,

is phenylene and Y is a divalent alkylene group of 1 to 20 carbon atoms, the subgenus of a,w-bis(2-benzothiazolyl)- This invention relates to the discovery that a,w-biS(2- alkanes defined having the frmula benzothiazolyl) -alkanes, -arylenes, or -polyalkanols, or (3) s s cr,wbis(2 benzimidazolyl)-alkanes, -arylenes or -polyalkanols inhibit the corrosion of metal, such as ferrous R c-(crn)mc metals, in acidic media, such as acidic solutions lllCllldlllg aqueous mineral acid solutions. The invention is based 15 N on the discovery that the aferenamed e p p wherein R and R are as previously defined and m has a ticularly such species as 1,4-bis(2-benzimidazolyl)butane value f 1 to and 1,2 bis (2-benzothiazolyl)ethane-1,2-diol compare w X is sulfur favorably in their abilities to protect metal surfaces against corrosion under the conditions of the standard 20 Static Corrosion Test with the best known inhibitors for A acid media such as the alkylpyridines. The invention also relates to the method of inhibiting the corrosion of metals in acid media by incorporating at least about 0.01 is phenylene, and Y is arylene of 6 carbon atoms, the wt. percent of the aforesaid compounds. The invention sub.genus of a w-bis(z-benzothiaxolyl) henylene i d also relates to non-corrosive aqueous acid compositions fi d,of th f l containing effective amounts of the compounds of this (4) S s invention. These and other discoveries and objectives of this invention will be described or become apparent as R C C the specification proceeds.

The corrgsipminhibitors of this invention are represented by compounds of the formula (I) X X whereinR and R are as previously defined and the relative position of the benzothiazolyl group attached to the phenylene group can be ortho, meta or para. Where X in each of the subgeneric Formulae 2, 3, 4 N N is imino the corresponding u,w-bis(Z-benzimidazolyl)- wherein R and R"are"the same or different substituents of polyalkanols (from Formula 2) and aw'blsa'benzlmlda' zoly1)phenylenes (from Formula 4) are defined. the group consisting of hydrogen, alkyl radicals of 1 to 20 40 1 t d t f carbon atoms, alkoxy radicals of 1 to 20 carbon atoms, t y. {on e f? a l g l f d at 10x radimmemon atoms; pa ent app 1cat1ons ase on is enz ot iazo y er1vat1ves y y as corrosion inhibitors In particular env1ronments; W namely, Serial No. 151,189, Nov. 9, 1961, and Serial No. 211,884, July 23, 1962, by Messrs. W. E. Kramer, R. C. (NT-) '45 Kimble, I. B. Braunwarth and the instant inventor. In is a divalent polyalkanol group of the f l copending application Serial No. 151,189 there is disclosed the discovery that the bisbenzothiazolyl polyhy- (CHOH)B' droxy alkanes; that is, compounds of Formula 2 herein, where n is 1 to 10, or a divalent alkylene group of 1 act as corrosion inhibitors for copper or copper-containto 20 carbon atoms, or a divalent arylene group of 6 to ing alloys in aerated aqueous detergent media. Applica- 14 cyclic carbon atoms; and tion Serial No. 211,884 by Messrs. W. E. Kramer, R. C.

Kimble and the instant inventor, discloses that the bisbenzimidazolyl alkanes of Formula 3 herein, when used A in amounts of from 0.0001 to 0.2 g./ 100 ml. of solution in aerated aqueous detergent media, inhibit the corrosion of copper or copper-containing alloys. These copending represents an aryl group of 6 to 14 cyclic carbon atomsapplications also disclose the manner of preparing these When X is sulfur, compounds.

The corrosive environments and the metal to be protected in said copending applications diifer markedly from A the corrosive environment and metal to be protected in accordance with this invention. As is known in the art, the protection of metals from the action of alkaline deis Phenylene and Y 18 golyalkanol h sub-genus of tergent solutions, particularly the protection of copper and pounds namepl My bis(2'benzothlazolyl)'polyalkanols its alloys from the corrosive action of commercial sulis defined havmg the formula fonate detergent preparations wherein the corrosion- (2) S S promoting ingredient is an alkali metal polyphosphate,

containing or not containing alkali metal sulfates, repre- R sents a peculiar problem, as does the protection of fer- 7O rous metals frorn'the corrosive action of acidic media, N N with which the instant invention is concerned. Even among preferred inhibitors of a given class there is considerable difference in ability to inhibit corrosion in a given environment, and the problem of finding an inhibitor which is as effective as the well-known and widely used amino or pyridinyl compounds for acid media is acute.

The following are selected species of compounds that are illustrative of the instant invention:

1,4-bis Z-benzimid azolyl butane l, l-bis Z-benzimid azolyl methane 1,20-bis 2-benzimidazolyl) eicosane 1,5-bis 2-benzimidazolyl pentane 1,2-bis(2-benzothiazolyl)ethane-1,2-diol 1,3-bis 2-benzothiazolyl propane- 1 ,2,3-triol 1,4-bis(Z-benzothiazolyl)butane-1,2,3 ,4-tetrol 1,2-bis 2-benzimid azolyl phenylene 1,3-bis Z-benzimidazolyl phenylene 1,4-bis 2-benzimidazolyl phenylene 1,8-bis (2-benzimidazolyl) anthrylene In order to demonstrate the invention the following experiments are presented.

Example I routine. The results are tabulated below:

Coneentra- Corrosion Additive tion (wt. Rate (inches percent) per year) None 0.137 1.4-bis(2-benzimidazolyl)butane. 0. 1 0.017 1,2-bis(2-benzothiazolyl)ethane-1,2-di 0. 1 0. 006 Alkylpyridine HB 0. 2 0. 0026 The above results show that the inhibitors of this invention compare favorably with alkylpyridines, which are among the best corrosion inhibitors known for acid media.

The inhibitors of this invention find utility in reducing the corrosion of ferrous metals in any acid media. By ferrous metals is meant such materials as cast iron, steel, alloys containing iron and the like. The acid medium may be any liquid or gaseous medium of an acid nature which is corrosive to ferrous metals. The acid component in the liquid or gaseous medium may be organic acid or an inorganic or mineral acid. The organic acids which are corrosive to ferrous metals are generally of low mTile'ciila r weight, such as acetic acid, binggigacid and the like, to include acids wfiiElT contain a group such as a halogen which functions to increase the activity of the hydrogen ion on the carboxyl group of the acids. Such acids include mono-, di-, and trichloro acetic acid, the corresponding chloro, bromo, and iodo acids having 1 to 5 carbon atoms in the alkyl portion of the acid, and related acids. The mineral or inorganic acid may be any of the commonly known acids such as sulfuric, hydrochloric, hydrobromic, hydroiodic, hydrofluoric, nitric, phosphoric, polyphosphoric, boric and related mineral acids. Mixtures of organic acids, or mixtures of inorganic acids and mixtures of bothmganiggid inorganic acids constitute the corrosive medium.

The amount of said corrosive acid in the corrosive medium is subject to variation depending on the nature of the ferrous metal in contact therewith. Under some circumstances, small concentrations in the order of .01 weight percent or volume percent may be exceedingly corrosive, particularly in the vapor state under elevated temperatures. Also, factors such as the velocity of flow of the vapor or liquid in contact with the ferrous metal to be protected come into consideration, as is known in this art. The upper concentration of the corrosive acid may be as high as 20 percent by weight in liquid phase and 20 volume percent in vapor phase.

Similarly, the oxygen content of the corrosive medium may vary, and generally the greatest corrosion rate is experienced with the maximum amount of oxygen present in accordance with its solubility under the existing conditions. Under some circumstances, the amount of oxygen may be quite low, in the order of .001 weight percent, and still cause considerable corrision due to constant replacement of the acid medium through flow of the vapors or liquid in contact with the ferrous metal.

Likewise, the temperature influences the rate of corrosion considerably and the additives of this invention are effective at low temperatures, in the order of 0 C. to as high as 200 C. Maximum effectiveness is obtained in combatting corrosion of aqueous inorganic acid solutions having concentrations of about 5 to 20 weight percent of acid at room temperature with oxygen being present at maximum amount soluble under these conditions.

The embodiments of the invention in which an exclusive property or privilege is claimed are described as follows.

I claim:

1. The method of protecting ferrous metals from corrosion in acidic media consisting of water containing about .01% to 20% by wt. of mineral acid which comprises maintaining in said acidic media about 0.01% by weight of a compound of the formula I C-YC/ wherein R and R' are substituents of the group consisting of hydrogen, C to C alkyl radicals, C to C alkoxy radicals and C to C aryloxy radicals, X is a substituent of the group consisting of sulfur and imino, Y is a substituent of the group consisting of a divalent polyalkanol of the formula where n is 1 to 10, a divalent C to C alkylene group, and a divalent C to C arylene group and represents an aryl group of 6 to 14 cyclic carbon atoms.

2. The method of preventing the corrosion of ferrous metals in contact with an aqueous solution containing about .01% to 20% by weight of hydrochloric acid which comprises maintaining about 0.1 weight percent of 1,2- bis(2-benzothiazolyl)ethane-1,2-diol in said aqueous solution.

3. An acidic composition, non-corrosive to metal surfaces in contact therewith, consisting essentially of water containing about 01% to 20% by wt. of mineral acid and as the sole corrosion-inhibiting component about 0.1 wt. percent of a compound of the formula wherein R and R are substituents of the group consisting of hydrogen, C to C alkyl radicals, C to C alkoxy radicals and C to C aryloxy radicals, X is a substituent of the group consisting of sulfur and imino, Y is a substituent of the group consisting of a divalent polyalkanol of the formula where n is 1 to 10, a divalent C to C alkylene group, and a diavlent C to C arylene group and 5. An acidic composition, non-corrosive to ferrous metal surfaces in contact therewith, consisting essentially of an aqueous solution containing about .01% to 20% by weight of hydrochloric acid and about 0.1 weight percent of l,2-bis(2-benzothiazolyl)ethane-1,2-diol.

6. The method of preventing the corrosion of ferrous metals in contact with an aqueous solution containing about .01% to 20% by weight of hydrochloric acid which comprises maintaining about 0.1% by weight of 1,4-bis(2- benzimidazolyl)butane in said aqueous solution.

References Cited by the Examiner UNITED STATES PATENTS 2,483,392 10/1949 Meyer et a1 260304 XR 2,832,735 4/1958 Hughes 252-8.55 2,985,661 5/ 1961' Hein et a1. 260-304 XR 3,105,837 10/1963 Ursprung 252391 XR JULIUS GREENWALD, Primary Examiner. 

1. THE METHOD OF PROTECTING FERROUS METALS FROM CORROSION IN ACIDIC MEDIA CONSISTING OF WATER CONTAINING ABOUT .01% TO 20% BY WT. OF MINERAL ACID WHICH COMPRISES MAINTAING IN SAID ACIDIC MEDIA ABOUT 0.01% BY WEIGHT OF A COMPOUND OF THE FORMULA 